问题补充：
Mary was caught in a traffic jam and by the time she arrived at the airport her father’s plane.
A. took off
B. had already taken off
C. was take off
D. had already been taken off
答案：
A. took off
(答案→)B. had already taken off
C. was take off
D. had already been taken off
解析：by the time与she arrived这一过去的动作连用，表示到过去那时为止已经完成的动作，用过去完成时。take off指“起飞”，没有被动语态。
